1. Field of the Invention
The present invention relates to an image processor for detecting incomplete articles, and more particularly to an image processor for detecting incomplete articles which is suitable for distinguishing complete from incomplete articles having complicated configurations, especially for inspecting articles for a lack of parts.
2. Statement of the Prior Art
Wire harnesses used in automobiles may be taken as an example of articles having complicated configurations.
Electrical equipment of various types are used in an automobile, and those having a relatively low electrical capacity are used in illumination, signalling, controlling, warning, charging and instrumentation systems, as well as for wind screen wipers.
The wiring for connecting this electrical equipment to a power supply is assembled on the relevant parts during one stage of an assembly line, and wire harnesses are components that are previously manufactured in such a manner as to enable such an assembly to be accomplished in a smooth fashion efficiently. Wire harnesses are formed from a number of electrical wires that are bundled together by utilizing vinyl tape or the like after being cut to predetermined lengths and harness parts (tubes, crampers, grommets, protectors, taping and so forth) which are mounted on the electrical wires.
Wire harnesses are normally produced by accurately placing bundled electrical wires on a plate with a representative drawing (plate on which a drawing showing how to assemble the relevant parts is placed thereon) and then mounting the necessary parts on the required portions of the bundled electrical wires while feeding the plate with a representative drawing forward on a production line.
Wire harnesses so assembled are then inspected for a lack of the necessary parts, and wire harnesses in which a lack of parts are found are rejected as incomplete articles.
Conventionally, visual inspection for a lack of parts in the articles has been done by eyesight. More recently visual inspection utilizing an image processing means has also been introduced to enhance the efficiency of the operation.
A conventional method of visually inspecting articles for a lack of parts thereof by utilizing an image processing means is described in FIG. 13 showing a schematic diagram of the constitution of a prior art image processor for detecting incomplete articles.
As seen from FIG. 13, a wire harness 1 is set on a plate with a representative drawing 2 that is adapted to travel in a direction shown by reference arrow A. Reference numeral 1a denotes a bundle of electric wires, and 1b denotes harness parts. The wire harness 1 and plate with a representative drawing 2 are imaged by an industrial camera 3, and video signals are sent to an image processor 4. This image processor 4 incorporates a television camera interface and a micro computer. The surface area of the plate with a representative drawing 2 is divided into a plurality of imaging regions each coinciding with the imaging field of the television camera 3, for instance, into four imaging regions divided by chain lines and designated by, respectively, reference numerals I, II, III and IV in the same figure. The video signals of the television camera 3 are sent to the image processor 4 every time the imaging field of the television camera 3 coincides with the respective imaging regions.
Images showing positions on which individual harness parts are normally placed and the normal configurations of the individual parts are registered in the image processor 4 via a terminal 5 (including a keyboard and a CRT), and this registration of images is conducted for the respective imaging regions. The image processor 4 has a monitor 6 connected thereto.
The image processor 4 detects the positions and configurations of the individual parts 1b of the wire harness 1 being inspected on the basis of the video signals sent thereinto and compares the detected actual positions and configurations with those of the registered images, thereby judging whether or not the individual necessary parts 1b are properly mounted on the wire harness.
Conducting a visual inspection of articles for a lack of parts by eyesight tends to exhaust the inspecting personnel, and also tends to be inaccurate.
The prior art visual inspection method utilizing an image processing means requires the normal positions and configurations of all of the harness parts 1b to be imaged so as to be registered. In order to successfully accomplish the image processing visual inspection, a tremendous amount of data must be registered and hence this requires an inordinately long period of time. In addition to this, a certain amount of time is required to complete the detection of the positions and configurations of the harness parts of the wire harness being inspected, and it is difficult to accurately detect the positions and configurations of the parts. Due to the above reasons, it is not possible to conduct an inspection simply and quickly with the prior art image processor.
In distinguishing complete articles from incomplete ones, reference values are normally provided in advance, and in the event of the detected values with respect to a product being inspected falling within the upper and lower limits of the reference value, the product is then judged as being complete. On the contrary, in the event of the detected values being smaller or greater than the lower or upper limits, respectively, the product is then judged as being incomplete. It may be easy to set reference values if there are only a few factors which the reference values govern. In the case of parts like wire harnesses which embody a wide variety of configurations and dimensions, the number of counted picture elements of a binarized image scatters even with a product judged to be a complete product. In addition, there are a number of different items to be inspected, and this makes it difficult to set accurate reference values to ensure a complete product and requires a tremendous amount of labor.
Referring further to FIG. 13, in a case where the wire harness 1 being inspected is long, it is hard to accurately locate the wire harness 1 under the industrial camera 3 by utilizing the technology shown and employed in the same figure. Moreover, the plate with a representative drawing 2 tends to slip from its initial position while being fed in the direction shown by reference arrow A, and once such a slippage occurs, it is not possible to make accurate judgements.
Furthermore, it is a well known fact that the lighting has a great effect on the results of an inspection when inspecting wire harnesses or the like by utilizing an image processing means. Therefore, the subject of the inspection must be illuminated in such a way as to allow it to clearly stand out against its background.
In order to accomplish such a way of lighting, a method in which the subject of the inspection is illuminated by transmitted light has generally been employed, and in this case, the subject in silhouette is imaged by means of a television camera disposed in front thereof.
However, transmitted light is not always usable due to external conditions. In a case where it is not possible to use transmitted light, the subject of the inspection is placed on a white board, and a light is also disposed in front of the subject as in the case of the television camera for illuminating the subject from the front thereof. The television camera is then allowed to image the brightly lit subject.
In this conventional technology, however, unnecessary shadows are produced on the white board since the subject is lit from the front thereof. In addition, in a case where there are patterns or characters on the white board, it is not possible to allow the subject to clearly stand out against the background without interference from these patterns or characters since they cannot be erased.